The excitation of surface plasmon-polariton (SPP) waveguide modes in 500-nm-wide and 550-nm-high dielectric
ridges deposited on a thin gold film is characterized at telecommunication wavelengths, by application of a
scanning near-field optical microscope (SNOM), and by utilizing the finite element method (FEM). Different
tapering structures for coupling in SPPs, excited at the bare gold-air interface, are investigated with a SNOM,
and the dependence of in coupling efficiency on tapering length is characterized by means of FEM calculations.
The performance of this in coupling method is compared to an alternative excitation scheme, where the effective
index of SPPs in the tapering region is matched to the index of the incident beam, thereby exciting SPPs directly
in the dielectric tapering structure. Single-mode guiding and strong lateral mode confinement of dielectric-loaded
SPP waveguide (DLSPPW) modes are demonstrated by characterizing a straight DLSPPW section with a SNOM
and with the effective index method (EIM). The propagation loss of DLSPPW modes is characterized for different
wavelengths in the telecommunication region, by application of a SNOM, and the results are compared to EIM
calculations.